α-acyloxy-β-amino-thiocarboxylic acid esters

ABSTRACT

The present invention provides a simple and inexpensive method for producing a-hydroxy-β-aminocarboxylic acids and their esters. An ester of an N-protected α-amino acid ester is converted into a β-ketosulfoxide, which is then processed with an acid to give an α-ketohemimercaptal. Next, this is acylated and then processed with a base to obtain an N-protected α-acyloxy-β-amino-thioester, which is then saponified to obtain an intended compound. According to the method of the present invention, it is possible to produce α-hydroxy-β-aminocarboxylic acid derivatives, which are intermediates in producing various HIV protease inhibitors, renin inhibitors and carcinostatics, from a-amino acids. The method comprises reduced reaction steps, the selectivity in the method to give the intended product is high, and the yield of the product obtained is high.

This is a division of application Ser. No. 08/725,714 filed on Oct. 4,1996, now U.S. Pat. No. 5,705,671.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to α-hydroxy-β-aminocarboxylic acidderivatives which are important as the ingredients constitutinginhibitors for enzymes, such as HIV protease and renin, or constitutingsome carcinostatics. In particular, the compounds of the presentinvention are important constituents of the HIV protease inhibitorKNI-272 (see Chem. Pharm. Bull., 40, 2251 (1992)), the renin inhibitorKRI-1314 (see J. Med. Chem., 33, 2707 (1990)), the carcinostaticBestatin (see Biochem. Pharmacol., 32, 1051 (1983)), and thecarcinostatic Taxol (see Bull. Cancer, 80, 326 (1993)); comprising, asthe constitutive ingredients, (2S,3S)-3-amino-2-hydroxy-4-phenylbutyricacid, (2R,3S)-3- amino-2-hydroxy-4-cyclohexylbutyric acid,(2S,3R)-3-amino-2-hydroxy-4-phenylbutyric acid, and(2R,3S)-phenylisoserine.

2. Discussion of the Background

Conventional methods for producing the above-mentioned compounds areknown and rely on, the corresponding α-amino acids as startingmaterials. The methods comprise preparing N-protected α-aminoaldehydesfrom the starting acids, reacting them with prussic acid derivatives togive cyanohydrin intermediates and hydrolyzing them at the cyano groupto obtain the intended compounds (see U.S. Pat. No. 4,599,198; Iizuka etal., J. Med. Chem., 33, 2707 (1990); M. T. Reets et al., TetrahedronLett., 29, 3295 (1988)). However, since these methods are defectivebecause they require an oxidation-reduction step, they use toxic cyanoderivatives and they produce, as intermediates, N-protectedα-aminoaldehydes which are unstable in quantity production. Accordingly,they are not suitable for the production of large quantities of thecompounds.

Another method is also known which comprises reacting a N-protectedα-aminoaldehyde with nitromethane through an aldol reaction in thepresence of an asymmetric catalyst, followed by hydrolyzing theresulting compound with an acid to obtain the intended product (seeEP-657415). However, this method is also unsuitable for large-scaleproduction of the product, since the intermediate α-aminoaldehyde isunstable and the asymmetric catalyst to be used is expensive.

Still another method is known which comprises reacting an N-protectedα-aminocarboxylic acid chloride to be derived from the correspondingα-amino acid with trimethylsilyl cyanide to give an α-oxonitrile, thenconverting it into an α-ketocarboxylate and thereafter reducing it toobtain the intended product (see EP-543343). However, this method isalso unsuitable to large-scale production of the product, since it usessuch an expensive and toxic cyano compound.

SUMMARY OF THE INVENTION

Accordingly, one object of the present invention is to provide anindustrial method for producing α-hydroxy-β-aminocarboxylic acids andtheir esters.

The present inventors have now found a method for stereoselectivelyproducing α-hydroxy-β-aminocarboxylic acids and their esters, whichcomprises reacting a β-ketosulfoxide that is easily obtained from anN-protected aminocarboxylate, with an acid to give anα-keto-hemimercaptal, then acylating it to give anα-keto-hemimercaptal-carboxylate, and thereafter rearranging it in thepresence of a base.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Specifically, the present invention is a method for producingα-acyloxy-thioesters of the formula (II): ##STR1## wherein R¹ representshydrogen, an unsubstituted or substituted linear, branched or cyclicalkanoyl group having from 2 to 18 carbon atoms; an unsubstituted orsubstituted linear, branched or cyclic alkoxycarbonyl group having from2 to 18 carbon atoms (such as t-butoxy carbonyl); an aralkyloxycarbonylgroup having from 7 to 18 carbon atoms (such as benzyloxycarbonyl); oran unsubstituted or substituted benzyl group, or represents, togetherwith R¹, a residue of a dibasic acid having from 8 to 18 carbon atoms;

R² represents a hydrogen atom or an optionally-substituted benzyl group,or represents, together with R¹ ', a residue of a dibasic acid havingfrom 8 to 18 carbon atoms;

R³ represents an unsubstituted or substituted, linear, branched orcyclic alkyl group having from 1 to 18 carbon atoms (such ascyclohexylmethyl or isobutyl), an aralkyl group having from 7 to 18carbon atoms (such as phenyl); or an aryl group having from 6 to 18carbon atoms (such as benzyl);

R⁴ represents an unsubstituted or substituted, linear, branched orcyclic alkanoyl group having from 2 to 18 carbon atoms (such as acetyl),or an arylcarbonyl group having from 7 to 18 carbon atoms (such asbenzoyl); and

R⁵ represents an alkyl group having 1 or 2 carbon atoms (such asmethyl), an aryl group having from 6 to 18 carbon atoms, or an aralkylgroup having from 7 to 18 carbon atoms,

which comprises rearranging, in the presence of a base, anα-keto-hemimercaptal-carboxylate of a general formula (I): ##STR2##wherein R¹, R², R³, R⁴ and R⁵ have the same meanings as above.

Compounds of the formula (I) can be obtained by

(i) reacting an N-protected α-aminocarboxylate of the formula (III):##STR3## wherein R¹, R² and R³ have the same meanings as above; and R⁶represents a linear or branched alkyl group having from 1 to 5 carbonatoms, an aryl group having from 6 to 18 carbon atoms, or an aralkylgroup having from 7 to 18 carbon atoms,

with a carbanion of a general formula (IV): ##STR4## wherein R⁵ has thesame meaning as above, to obtain a β-ketosulfoxide of the formula (V):##STR5## wherein R¹, R², R³ and R⁵ have the same meanings as above,

(ii) then reacting the sulfoxide with an acid to obtain anα-ketohemimercaptal of a general formula (VI): ##STR6## wherein R¹, R²,R³ and R⁵ have the same meanings as above, and thereafter

(iii) acylating the hemimercaptal.

N-protected α-aminocarboxylates (III) which are used in the presentinvention can be derived from α-aminocarboxylic acids according toconventional means used in ordinary peptide synthesis. Theα-aminocarboxylic acids may be naturally-existing amino acids orsynthetic amino acids. Their esters are represented by the followingstructural formula: ##STR7## wherein R³ represents an unsubstituted orsubstituted, linear, branched or cyclic alkyl group having from 1 to 18carbon atoms, an aralkyl group having from 7 to 18 carbon atoms, or anaryl group having from 6 to 18 carbon atoms. Suitable examples includebenzyl, cyclohexyl-methyl, phenyl, isopropyl, isobutyl and sec-butylgroups. Suitable amino acid moieties include, for example,phenylalanine, cyclohexylalanine, phenylglycine, valine, leucine andisoleucine.

R¹ and R² in the N-protected α-aminocarboxylates (III) areamino-protecting groups or are the protected condition of the esters.The protecting groups are not specifically defined but may be any onesthat are used in ordinary peptide synthesis. For example, R¹ may be anunsubstituted or substituted, linear, branched or cyclic alkanoyl grouphaving from 2 to 18 carbon atoms, an unsubstituted or substituted,linear, branched or cyclic alkoxycarbonyl group having from 2 to 18carbon atoms, an aralkyloxycarbonyl group having from 7 to 18 carbonatoms, or an unsubstituted or substituted benzyl group, or may be,together with R², a residue of a dibasic acid having from 8 to 18 carbonatoms R² may be a hydrogen atom or an unsubstituted or substitutedbenzyl group, or may be, together with R², a residue of a dibasic acidhaving from 8 to 18 carbon atoms. Namely, R¹ and R² each areindependently a hydrogen atom or an amino-protecting group, or theyform, as combined, a bifunctional, amino-protecting group. Theamino-protecting group includes, for example, so-called, urethane-typeprotecting groups such as a benzyloxycarbonyl group and at-butyloxycarbonyl group; acyl-type protecting groups such as an acetylgroup and a benzoyl group; and a benzyl-type protecting groups such as abenzyl group and a dibenzyl group. One example of the bifunctionalamino-protecting group is a phthaloyl group.

R⁶ in the N-protected α-aminocarboxylates (III) indicates an esterresidue of an amino acid. R⁶ may be a linear or branched alkyl grouphaving from 1 to 5 carbon atoms (such as methyl or ethyl), an aryl grouphaving from 6 to 18 carbon atoms (such as benzyl), or an aralkyl grouphaving from 7 to 18 carbon atoms. Suitable examples include methyl,ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, t-butyl and benzylgroups.

The reaction of the N-protected α-aminocarboxylate (III) with thecarbanion (IV) to give the β-ketosulfoxide (V) may be conducted bydissolving the N-protected α-aminocarboxylate in an inert solvent suchas tetrahydrofuran, diethyl ether or methyl t-butyl ether, followed bydropwise adding the resulting solution to a solution of a carbanion ofmethylsulfoxide as prepared in the manner as mentioned below. Thetemperature at which the former solution is dropwise added to the lattersolution may fall between -70° C. and 20° C., preferably between -20° C.and 10° C. The reaction temperature may fall between -70° C. and 20° C.,preferably between -20° C. and 10° C. Typically, 2.0 to 5.0 equivalentsof the carbanion (IV) and 2.0 to 5.0 equivalents of base are used perequivalent of N-protected α-amino-carboxylate (III).¹

The carbanion can be prepared by reacting a methylsulfoxide of theformula (III') with a base. ##STR8##

R⁵ in the methylsulfoxide of formula (III') represents an alkyl grouphaving 1 or 2 carbon atoms, an aryl group having from 6 to 18 carbonatoms, or an aralkyl group having from 7 to 18 carbon atoms. Specificexamples of the methylsulfoxide include dimethylsulfoxide,methylethylsulfoxide, methylphenylsulfoxide, andmethyl-p-tolylsulfoxide. Of these, preferred is dimethylsulfoxide inview of the economical aspect and the easy availability.

To prepare the anion, any and every base capable of forming it can beemployed. Preferred base include sodium amide, sodium hydride, potassiumt-butoxide and lithium diisopropylamide. The anion is suitably preparedin an inert solvent such as dimethylsulfoxide, tetrahydrofuran, diethylether or methyl t-butyl ether or a mixture thereof.

The temperature at which the anion is prepared falls between -70° C. and80° C., preferably between -20° C. and 70° C. The time to be taken forthe preparation may be approximately from 30 minutes to 2 hours. Theconcentration of the anion thus prepared may be approximately from 0.5mol/liter to 5 mol/liter.

To post-treat the reaction mixture, it is poured into an aqueous, acidicsolution or, alternatively, the latter is poured into the former. Theaqueous, acidic solution may be, for example, an aqueous solution ofcitric acid, acetic acid or hydrochloric acid.

The reaction gives a second asymmetric center on the sulfur atom in theproduct, which, therefore, generally consists of two diastereomers ortwo pairs of diastereomers depending on the starting compound, either aracemic amino acid derivative or an optically-active amino acidderivative. These diastereomers can be used in the next reaction withoutbeing specifically isolated. When used to produce theα-ketohemimercaptal (VI) in the next reaction, the β-keto-sulfoxide neednot be purified but a crude product or a non-processed reaction mixturecomprising it can be directly used in the next reaction.β-ketosulfoxides (V) as produced after the reaction are novel compounds.

To obtain α-keto-hemimercaptals (VI) by reacting the ketosulfoxide (V)as obtained in the above with an acid, for example, the β-ketosulfoxideis dissolved in a water-soluble solvent, such as dimethylsulfoxide,dimethylformamide, tetrahydrofuran, dioxane, or alcohol (e.g., methanol,ethanol), and then an aqueous solution of an acid, such as hydrochloricacid, sulfuric acid, hydrobromic acid or p-toluenesulfonic acid is addedthereto and reacted at from -20° C. to 50° C. The reaction solvent ispreferably dimethylsulfoxide, and the acid is preferably hydrochloricacid, since few side reactions occur. The reaction temperature ispreferably from 0° C. to 30° C.

α-keto-hemimercaptals can also be obtained by reacting theβ-ketosulfoxide with an acid anhydride followed by hydrolyzing theproduct. The solvent usable in the reaction includes, for example,dichloromethane, chloroform, tetrahydrofuran, dioxane, diethyl ether,dimethylformamide, dimethylacetamide, pyridine, toluene and ethylacetate. The acid anhydride includes, for example, acetic anhydride,triflucroacetic anhydride and trichloroacetic anhydride. In order tosmoothly carry out the reaction, a base, such as pyridine, 2-picoline,2,6-lutidine, 2,4,6-collidine or triethylamine, can be added to thereaction system.

In the next reaction of acylating the hydroxyl group of theα-keto-hemimercaptal (VI) to give the α-keto-hemimercaptalcarboxylate(I), the α-keto-hemimercaptal is dissolved in a solvent which isgenerally used in ordinary acylation, such as dichloromethane,chloroform, tetrahydrofuran, dioxane, diethyl ether, dimethylformamide,dimethylacetamide, pyridine, toluene or ethyl acetate, and then treatedwith an acylating agent. The acylating agent may be selected from acidchlorides, acid bromides and acid anhydrides. Suitable examples includeacetyl chloride, acetic anhydride, benzoyl chloride and benzoyl bromide.In order to smoothly carry out the reaction, a base, such as pyridine,2-picoline, 2, 6-lutidine, 2,4,6-collidine or triethylamine, can beadded to the reaction system. The reaction temperature may be from -50°C. to 50° C. but is preferably from -20° C. to 30° C.

α-keto-hemimercaptal-carboxylates (I) can also be obtained by reactingthe β-ketosulfoxide (V) with an acid anhydride. The solvent usable inthe reaction includes, for example, dichloromethane, chloroform,tetrahydrofuran, dioxane, diethyl ether, dimethylformamide,dimethylacetamide, pyridine, toluene and ethyl acetate. The acidanhydride includes, for example, acetic anhydride and trichloroaceticanhydride. In order to smoothly carry out the reaction, a base, such aspyridine, 2-picoline, 2,6-lutidine, 2,4,6-collidine or triethylamine,can be added to the reaction system.

The α-keto-hemimercaptal-carboxylate prepared as above is rearranged inthe presence of a base into a β-amino-α-acyloxy-thioester (II). The baseincludes, for example, 1,8-diazabicyclo 5.4.0!undec-7-ene,1,5-diazabicyclo 4.3.0!non-5-ene, 4-dimethylaminopyridine, pyridine,2-picoline, 2,6-lutidine, 2,4,6-collidine, triethylamine anddiisopropylethylamine. Of these, preferred are 1,8-diazabicyclo5.4.0!undec-7-ene and 1,5-diazabicyclo 4.3.0!non-5-ene. The solventusable in the reaction includes, for example, dichloromethane,chloroform, tetrahydrofuran, dioxane, diethyl ether, dimethylformamide,dimethylacetamide, dimethylsulfoxide, pyridine, toluene, ethyl acetate,methanol, ethanol, isopropanol and t-butanol.

The reaction temperature may be from -80° C. to 50° C., but, in general,the diastereoselectivity in the reaction is higher at lower reactiontemperatures.

The reaction also gives a second asymmetric center in the product, whichgenerally consists of two diastereomers or two pairs of diastereomersdepending on the starting compound, either a racemic amino acidderivative or an optically-active amino acid derivative. The ratio ofthe diastereomers formed or, that is, the diastereoselectivity varies,depending on the solvent used and the reaction temperature.

The diastereomers can be isolated, for example, through columnchromatography or crystallization.

The compound as produced according to the method of the presentinvention has two asymmetric centers (if R¹ and R² do not have anyadditional asymmetric center) and therefore includes four stereoisomers.Only one of the two asymmetric centers is formed through the reaction inthe method of the present invention, while the stereo-configuration withrespect to the other asymmetric center is kept as such throughout themethod. Therefore, when an optically-active α-amino derivative is usedas the starting compound in the method of the present invention, italways gives a mixture of two diastereomers. Because these havedifferent physical properties, these two diastereomers can be separatedfrom each other. Accordingly, the present invention is especiallyadvantageous in producing α-hydroxy-β-amino acids having the samestereo-configuration.

α-carboxy-thioesters (II) as obtained after the above-mentioned reactioncan be hydrolyzed or alcoholyzed into N-protectedβ-amino-α-hydroxycarboxylic acids or their esters of the formula (VII):##STR9## wherein R¹, R² and R³ have the same meanings as above; and R⁷represents a hydrogen atom, an alkyl group having from 1 to 8 carbonatoms, an aryl group having from 6 to 18 carbon atoms, or an aralkylgroup having from 7 to 18 carbon atoms.

The solvent usable in the hydrolysis includes, for example, alcoholicsolvents such as methanol, ethanol and 2-propanol, and mixed solventscomprising tetrahydrofuran or dioxane, and water. The reagent to be usedin the reaction is a metal hydroxide, preferably sodium hydroxide orpotassium hydroxide. The reaction temperature may fall between -20° C.and 80° C., but preferably between 0° C. and 40° C. Typically, 1.0 to2.0, preferably 1.2, equivalents of the solvent may be used.

The solvent usable in the alcoholysis may be an alcohol corresponding tothe intended ester, preferably methanol or ethanol. The base to be usedin the reaction includes, for example, metal alkoxides, preferablysodium methoxide and sodium ethoxide; metal hydroxides, preferablysodium hydroxide and potassium hydroxide; and metal carbonates,preferably sodium carbonate and potassium carbonate.

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples which are providedherein for purposes of illustration only and are not intended to belimiting unless otherwise specified.

EXAMPLES Example 1

Production of N,N-dibenzyl-(L)-phenylalanine benzyl ester:

25.Og (151.3 mmol) of (L)-phenylalanine and 66.67 g (482.4 mmol) ofpotassium carbonate were dissolved in 100 ml of water, and then 57.51 g(454.3 mmol) of benzyl chloride was added thereto and stirred under heatat 95° C. for 19 hours. After having been cooled to room temperature,this was subjected to phase separation with 67 ml of n-heptane and 50 mlof water. The organic layer thus separated was washed two times with 50ml of a solution of methanol/water (=1/2) and then dried with anhydroussodium sulfate. This was filtered and concentrated to obtain 61.64 g(90.5 wt. %, 121.8 mmol) of the above-entitled compound. The yield was84.7%.

¹ H-NMR (300 MHz, CDC1₃)

δ: 3.00 (dd, 1H), 3.14 (dd, 1H), 3.53 (d, 2H), 3,71 (t, 1H), 3.92 (d,2H), 5.12 (d, 1H), 5.23 (d, 1H), 6.99-7.40 (m, 20H).

Mass spectrum (FAB) 436 (MH⁺)

Example 2

Production of(3S)-3-(N,N-dibenzyl)amino-1-methylsulfinyl-2-oxo-4-phenylbutane:

3.76 g (96.39 mmol) of sodium amide was suspended in 40 ml ofdimethylsulfoxide and heated at from 74° to 75° C. for 30 minutes. 40 mlof tetrahydrofuran was added to the resulting solution and cooled to 0°C. To this was dropwise added a solution of 15.47 g (90.5 wt. %, 32.14mmol) of N,N-dibenzyl-(L)-phenylalanine benzyl ester as dissolved in 20ml of tetrahydrofuran, while keeping it at 0° C. After these werereacted at 0° C. for 30 minutes, 120 ml of an aqueous solution of 10%citric acid and 100 ml of ethyl acetate were added to the reactionmixture, which was thus subjected to phase separation. The aqueous layerthus separated was extracted once with 50 ml of ethyl acetate, and theresulting extract was combined with the previously-separated organiclayer and then washed with 60 ml of a saturated saline solution. Thiswas dried with anhydrous sodium sulfate, filtered and concentrated, andthe resulting residue was purified through silica gel columnchromatography (hexane/ethyl acetate=from 2/1 to 1/3) and thencrystallized in toluene/hexane to obtain 11.16 g of the above-entitledcompound. The yield was 85.6%. The integral ratio in ¹ H-NMR of thecompound verified that the ratio of the diastereomers constituting it isabout 1:1.

¹ H-NMR (300 MHz, CDC1₃)

δ2.27 (s, 3/2H), 2.35 (s, 3/2H), 2.97 (dd, 1H), 3.14 (dd, 1/2H), 3.19(dd, 1/2H), 3.55-3.65 (m, 7/2H), 3.75 (d, 1/2H), 3.85 (d, 2H), 4.01 (d,1/2H), 4.07 (d, 1/2H), 7.10-7.40 (m, 15H).

Mass spectrum (FAB) 406 (MH⁺)

Example 3

Production of(3S)-3-(N,N-dibenzyl)amino-1-hydroxy-1-methylthio-2-oxo-4-phenylbutane:

309.6 mg (0.763 mmol) of(3S)-3-(N,N-dibenzyl)amino-1-methylsulfinyl-2-oxo-4-phenylbutane wasdissolved in 6 ml of dimethylsulfoxide, and 1.5 ml of 2N hydrochloricacid was added thereto and stirred at room temperature for 16 hours.While being cooled in an ice bath, this was neutralized with 5 ml of asaturated aqueous solution of sodium hydrogen carbonate, and thensubjected to phase separation with 20 ml of ethyl acetate and 10 ml ofwater. The resulting aqueous layer was extracted twice with 10 ml ofethyl acetate. The organic layers were combined, then washed with 20 mlof water and 20 ml of a saturated saline solution in that order, andthereafter dried with anhydrous sodium sulfate. This was filtered andconcentrated to obtain 371.5 mg of a crude product of the above-entitledcompound.

¹ H-NMR (300 MHz, CDC1₃)

δ1.13 (s, 3H), 3.05 (dd, 1H), 3.18 (dd, 1H), 3.52 (d, 2H), 3.82 (d, 2H),4.24 (dd, 1H), 5.44 (d, 1H), 7.12-7.38 (m, 15H)

Example 4

Production of(3S)-1-acetoxy-3-(N,N-dibenzyl)amino-1-methyl-thio-2-oxo-4-phenylbutane:

173.0 mg of the crude product of (3S)-3-(N,N-dibenzyl)amino-1-hydroxy-1-methylthio-2-oxo-4-phenylbutane as obtained in Example3 was dissolved in 4 ml of dichloromethane and 0.1 ml of pyridine, and0.05 ml (0.703 mmol) of acetyl chloride was added thereto, while coolingin an ice bath, and stirred at room temperature for 30 minutes. Thereaction mixture was extracted with 5 ml of 0.2N hydrochloric acid and10 ml of dichloromethane as added thereto. The resulting organic layerwas washed with 5 ml of a saturated aqueous solution of sodium hydrogencarbonate and 8 ml of a saturated saline solution, and then dried withanhydrous sodium sulfate. This was filtered and concentrated, and theresulting residue was purified through partitioning, silica gelthin-layer chromatography to obtain 144.8 mg (0.324 mmol) of theabove-entitled compound. The yield was 91.1% (two steps). The integralratio in ¹ H-NMR of the compound verified that the compound is a mixtureof diastereomers of about 20:1. The data of the major diastereomer areshown below. ¹ H-NMR (300 MHz, CDC1₃)

δ: 1.18 (s, 3H), 2.14 (s, 3H), 3.03 (dd, 1H), 3.17 (1H, dd), 3.54 (d,2H), 3.87 (d, 2H), 4.22 (dd, 1H), 6.41 (s,1H), 7.10-7.40 (m, 15H).

Mass spectrum (FAB) 448 (MH⁺)

Example 5

Production of methylthio(3S)-(2R,S)-2-acetoxy-3-(N,N-dibenzyl)amino-4-phenylbutyrate:

89.5 mg (0.200 mmol) of (3S)-1-acetoxy-3-(N,N-dibenzyl)amino-1-methylthio-2-oxo-4-phenylbutane was dissolved in 2 ml of tolueneand cooled to -30° C., and 0.03 ml (0.201 mmol) of 1,8-diazabicyclo5.4.0!undec-7-ene was added thereto. After having been stirred at -30°C. for 23 hours, this was extracted with 7 ml of toluene and 6 ml of0.2N hydrochloric. The resulting organic layer was washed with 5 ml of asaturated aqueous solution of sodium hydrogen carbonate and 5 ml of asaturated saline solution, then dried with anhydrous sodium sulfate,filtered and concentrated. The resulting residue was purified throughpartitioning, silica gel thin-layer chromatography to obtain 95.6 mg(0.214 mmol) of the above-entitled compound. The yield was 106.8%. Theintegral ratio in ¹ H-NMR of the compound verified that the ratio of thediastereomers constituting it, of (2S,3S):(2R,3S) is about 58:42.

(2S,3S) diastereomer:

¹ H-NMR (300 MHz, CDC1₃)

δ: 2.23 (s, 3H), 2.24 (s, 3H), 2.80 (dd, 1H), 3.08 (dd,1H), 3.39 (d,2H), 3.65 (ddd, 1H), 3.88 (d, 2H), 5.83 (d,1H), 6.96-7.30 (m, 15H).

Mass spectrum (FAB) 448 (MH⁺)

(2R,3S) diastereomer:

¹ H-NMR (300 MHz, CDC1₃)

δ: 2.23 (s, 3H), 2.24 (s, 3H), 2.81 (dd, 1H), 3.10 (dd,1H), 3.56 (d,2H), 3.59 (m, 1H), 4.04 (d, 2H), 5.07 (d,1H), 6.96-7.30 (m, 15H).

Mass spectrum (FAB) 448 (MH⁺)

Example 6

Production of methylthio(3S)-(2R,S)-2-acetoxy-3-(N,N-dibenzyl)amino-4-phenylbutyrate:

50.6 mg (0.113 mmol) of (3S)-1-acetoxy-3-(N,N-dibenzyl)amino-1-methylthio-2-oxo-4-phenylbutane was dissolved in 1.1 ml ofdimethylformamide and cooled to -30° C., and 0.02 ml (0.134 mmol) of1,8-diazabicyclo 5.4.0!undec-7-ene was added thereto. After having beenstirred at -30° C. for 1 hour and 15 minutes, this was extracted with 10ml of ethyl acetate and 6 ml of 0.2N hydrochloric acid. The resultingorganic layer was washed with 6 ml of water and 8 ml of a saturatedsaline solution, then dried with anhydrous sodium sulfate, filtered andconcentrated. The resulting residue was purified through partitioning,silica gel thin-layer chromatography to obtain 44.6 mg (0.100 mmol) ofthe above-entitled compound. The yield was 88.2%. The integral ratio in¹ H-NMR of the compound verified that the ratio of the diastereomersconstituting it, of (2S,3S):(2R,3S), is about 92:8.

Example 7

Production of(3S)-1-benzoxy-3-(N,N-dibenzyl)amino-1-methyl-thio-2-oxo-4-phenylbutane:

671.2 mg (1.655 mmol) of(3S)-3-(N,N-dibenzyl)amino-1-methylsulfinyl-2-oxo-4-phenylbutane wasdissolved in 10 ml of dimethylsulfoxide and 7 ml of tetrahydrofuran, and5 ml of 2N hydrochloric acid was added thereto and stirred at roomtemperature for 15 hours. While being cooled in an ice bath, this wasneutralized with 15 ml of a saturated aqueous solution of sodiumhydrogen carbonate, and then subjected to phase separation with 50 ml ofethyl acetate and 50 ml of water as added thereto. The resulting aqueouslayer was extracted twice with 25 ml of ethyl acetate. The organiclayers were combined, washed with 50 ml of water and 50 ml of asaturated saline solution in that order, and then dried with anhydroussodium sulfate. This was filtered and concentrated to obtain 371.5 mg ofa crude product.

The crude product was dissolved in 17 ml of dichloromethane and 0.67 mlof pyridine, and 0.23 ml (1.95 mmol) of benzoyl bromide was addedthereto, while cooling it in an ice bath, and then stirred at roomtemperature for 35 minutes. The reaction mixture was extracted with 20ml of 5N hydrochloric acid and 20 ml of dichloromethane as addedthereto. The resulting organic layer was washed with 15 ml of asaturated aqueous solution of sodium, hydrogen carbonate and 20 ml of asaturated saline solution, and the dried with anhydrous sodium sulfate.This was filtered and concentrated, and the resulting residue waspurified through silica gel column chromatography (hexane/ethylacetate=from 15/1 to 10/1) to obtain 774.3 mg (1.519 mmol) of theabove-entitled compound. The yield was 91.8% (two steps). The integralratio in ¹ H-NMR of the compound verified that the compound is a mixtureof diastereomers of about 13:1. The data of the major diastereomer areshown below. ¹ H-NMR (300 MHz, CDC1₃)

δ: 1.31 (s, 3H), 3.05 (dd, 1H), 3.20 (dd, 1H), 3.57 (d,2H), 3.91 (d,2H), 4.27 (dd, 1H), 6.66 (s, 1H), 7.12-7.60 (m, 18H), 8.06-8.10 (m, 2H).

Mass spectrum (FAB) 510 (MH⁺)

Example 8

Production of methylthio(3S)-(2R,S)-2-benzoxy-3-(N,N-dibenzyl)amino-4-phenylbutyrate:

54.2 mg (0.106 mmol) of(3S)-1-benzoxy-3-N,N-dibenzylamino-1-methylthio-2-oxo-4-phenylbutane wasdissolved in 1.1 ml of toluene and cooled to 0° C., and 0.03 ml (0.201mmol) of 1,8-diazabicyclo 5.4.0!undec-7-ene was added thereto. Afterhaving been stirred at 0° C. for 2 hours and 20 minutes, this wasextracted with 10 ml of toluene and 6 ml of 0.2N hydrochloric acid asadded thereto. The resulting organic layer was washed with 5 ml ofwater, 5 ml of a saturated aqueous solution of sodium hydrogen carbonateand 5 ml of a saturated saline solution, then dried with anhydroussodium sulfate, filtered and concentrated. The resulting residue waspurified through partitioning, silica gel thin-layer chromatography toobtain 45.0 mg (0.088 mmols) of the above-entitled compound. The yieldwas 83.3%. The integral ratio in ¹ H-NMR of the compound verified thatthe ratio of the diastereomers constituting it, of (2S,3S):(2R,3S), isabout 50:50.

(2S,3S) diastereomer:

¹ H-NMR (300 MHz, CDC1₃)

δ: 2.23 (s, 3H), 2.97 (dd, 1H), 3.22 (dd, 1H), 3.43 (d,2H), 3.78 (m,1H), 3.93 (d, 2H), 6.11 (d, 1H), 7.01-7.26 (m, 15H), 7.50-7.56 (m, 2H),7.63-7.68 (m, 1H), 8.17-8.19 (m, 2H).

Mass spectrum (FAB) 510 (MH⁺)

(2R,3S) diastereomer:

¹ H-NMR (300 MHz, CDC1₃)

δ: 2.24 (s, 3H), 2.90 (dd, 1H), 3.15 (dd, 1H), 3.65 (d,2H), 3.74 (m,1H), 4.15 (d, 2H), 5.37 (d, 1H), 7.02-7.05 (m, 2H), 7.19-7.37 (m, 13H),7.43-7.48 (m, 2H), 7.58.8.63 (m, 1H), 8.09-8.12 (m, 2H).

Mass spectrum (FAB) 510 (MH⁺)

The mixture of diastereomers as obtained in Example 8 was crystallizedin ethyl acetate/hexane to give only crystals of the (2R,3S)diastereomer.

Example 9

Production of methylthio(3S)-(2R.S)-2-benzoxy-3-(N,N-dibenzyl)amino-4-phenylbutyrate:

54.2 mg (0.106 mmol) of (3S)-1-benzoxy-3-(N,N-dibenzyl)amino-1-methylthio-2-oxo-4-phenylbutane was dissolved in 1.1 ml ofdimethylformamide and cooled to -30° C., and 0.02 ml (0.134 mmol) of1,8-diazabicyclo 5.4.0!undec-7-ene was added thereto. After having beenstirred at -30° C. for 30 minutes, this was extracted with 15 ml ofethyl acetate and 10 ml of 0.2N hydrochloric acid as added thereto. Theresulting organic layer was washed with 10 ml of water and 8 ml of asaturated saline solution, then dried with anhydrous sodium sulfate,filtered and concentrated. The resulting residue was purified throughpartitioning, silica gel thin-layer chromatography to obtain 50.1 mg(0.098 mols) of the above-entitled compound. The yield was 83.3%. Theintegral ratio in ¹ H-NMR of the compound verified that the ratio of thediastereomers constituting it, of (2S,3S):(2R,3S), is about 87:13.

Example 10

Production of(3S)-(2R,S)-3-(N,N-dibenzyl)amino-2-hydroxy-4-Phenylbutyric acid:

87.1 mg (0.171 mmol) of methylthio(3S)-(2R,S)-2-benzoxy-3-N,N-dibenzylamino-4-phenylbutyrate was dissolvedin 1.7 ml of tetrahydrofuran, and 0.68 ml of an aqueous solution of 1Nsodium hydroxide was added thereto and stirred at room temperature for 2days. After having been concentrated, this was subjected to phaseseparation with 2 ml of water, 7 ml of dichloromethane and 0.68 ml of 1Nhydrochloric acid was added thereto. The resulting aqueous layer wasextracted twice with 4 ml of dichloromethane. The organic layers werecombined and dried with anhydrous sodium sulfate, then filtered andconcentrated, and the resulting residue was purified throughpartitioning, silica gel thin-layer chromatography to obtain 44.9 mg ofthe above-entitled compound. The yield was 69.9 Mass spectrum (FAB) 376(MH⁺)

Example 11

Production of methyl(3S)-(2R,S)-3-N,N-dibenzvlamino-2-hydroxy-4-phenylbutyrate:

53.6 mg (0.105 mmol) of methylthio(3S)-(2R,S)-2-benzoxy-3-N,N-dibenzylamino-4-phenylbutyrate was dissolvedin 2 ml of methanol and 0.5 ml of tetrahydrofuran, and 0.04 ml of sodiummethoxide (28% methanolic solution) was added thereto and stirred atroom temperature for 3 hours and 20 minutes. After having beenconcentrated, this was subjected to phase separation with 20 ml of ethylacetate, 5 ml of water and 0.5 ml of 1N hydrochloric acid as addedthereto. The resulting organic layer was washed with a saturated salinesolution. This was dried with anhydrous sodium sulfate, then filteredand concentrated, and the resulting residue was purified throughpartitioning, silica gel thin-layer chromatography to obtain 9.8 mg(0.0252 mmol; yield 24.0%) of (2S,3S) diastereomer of the above-entitledcompound and 4.5 mg (0.0116 mmol; yield 11.0%) of (2R,3S) diastereomerthereof.

¹ H-NMR (300 MHz, CDC1₃)

δ: 2.81 (dd, 1H), 3.03 (dd, 1H), 3.10 (br. d, 1H, --OH), 3.42 (dt, 1H),3.53 (s, 3H), 3.66 (d, 2H), 3.8 1 (d, 2H), 4.48 (m, 1H), 7.05-7.29 (m,15H).

Mass spectrum (FAB) 390 (MH⁺)

(2R,3S) diastereomer:

¹ H-NMR (300 MHz, CDC1₃)

δ: 3.05-3.24 (m, 4H), 3.41 (s, 3H), 3.46 (d, 2H), 4.00 (br. t, 1H), 4.12(d, 2H), 7.19-7.35 (m, 15H).

Mass spectrum (FAB) 390 (MH⁺)

Example 12

Production of N-benzyloxycarbonyl-(L)-phenylalanine methyl ester:

20.0 g (92.73 mmol) of (L)-phenylalanine methyl ester hydrochloride wassuspended in 93 ml of toluene, and 15.82 g (92.73 mmols) of benzylchloroformate was added thereto. 130 ml of an aqueous solution of 1Msodium carbonate was dropwise added thereto, while keeping it at 7° C.or lower, and stirred for 3 hours. After this was subjected to phaseseparation, the resulting organic layer was washed with 60 ml of 0.1Nhydrochloric acid and 60 ml of a saturated aqueous solution of sodiumhydrogen carbonate, and then dried with anhydrous sodium sulfate. Thiswas filtered and concentrated to obtain 28.75 g (96.8 wt. %, 88.81 mmol)of the above-entitled compound. The yield was 95.8%.

¹ H-NMR (300 MHz, CDC1₃)

δ: 3.11 (m, 2H), 3.72 (s, 3H), 4.66 (m, 1H), 5.09 (s,2H), 5.21 (br. d,1H, --NH), 7.08-7.39 (m, 1OH).

Mass spectrum (FAB) 314 (MH⁺)

Example 13

Production of(3S)-3-(N-benzyloxycarbonyl)amino-1-methylsulfinyl-2-oxo-4-phenylbutane:

4.98 g (127.7 mmol) of sodium amide was suspended in 40 ml ofdimethylsulfoxide and heated at from 72° to 76° C. for 50 minutes. 50 mlof tetrahydrofuran was added thereto and cooled to 0° C. To this wasdropwise added a solution of 10.33 g (96.8 wt. %, 31.91 mmol) ofN-benzyloxycarbonyl-(L)-phenylalanine methyl ester as dissolved in 20 mlof tetrahydrofuran, while keeping it at 0° C. After these were reactedat 0° C. for 1 hour, the reaction mixture was extracted with 120 ml ofan aqueous solution of 10% citric acid and 100 ml of dichloromethane asadded thereto. The resulting aqueous layer was extracted once with 60 mlof dichloromethane. The resulting organic layers were combined andwashed with 80 ml of a saturated saline solution. This was dried withanhydrous sodium sulfate, then filtered and concentrated, and theresulting residue was crystallized in dichloromethane/hexane to obtain8.14 g (22.65 mmols) of the above-entitled compound. The yield was71.0%. The integral ratio in ¹ H-NMR of the compound verified that thecompound is a mixture of diastereomers of about 3:1.

¹ H-NMR (300 MHz, CDC1₃)

δ: 2.63 (s, 3/4H), 2.66 (s, 9/4H), 2.94-3.01 (m, 1H), 3.12-3.21 (m, 1H),3.57 (d, 3/4H), 3.69 (d, 1/4H), 3.89 (d, 1/4H), 4.04 (d, 3/4H),4.45-4.59 (m, 1H), 5.07 (m,2H), 5.44 (br. d, 1/4H), 5.64 (br. s, 3/4H),7.14-7.39 (m, 1OH).

Mass spectrum (FAB) 360 (MH⁺)

Example 14

Production of(3S)-3-(N-benzyloxycarbonyl)amino-1-hydroxy-1-methylthio-2-oxo-4-phenylbutane:

708.6 mg (1.971 mmol) of(3S)-3-N-benzyloxycarbonylamino-1-methylsulfinyl-2-oxo-4-phenylbutanewas dissolved in 15 ml of dimethylsulfoxide and 6 ml of tetrahydrofuran,and 7.5 ml of 2N hydrochloric acid was added thereto and stirred at roomtemperature for 18 hours. While being cooled in an ice bath, this wasneutralized with 15 ml of a saturated aqueous solution of sodiumhydrogen carbonate, and then subjected to phase separation with 50 ml ofethyl acetate and 50 ml of water. The resulting aqueous layer wasextracted twice with 25 ml of ethyl acetate. The organic layers werecombined, washed with 50 ml of water and 30 ml of a saturated salinesolution in that order, and then dried with anhydrous sodium sulfate.This was filtered and concentrated, and the resulting residue wascrystallized in hexane/ethyl acetate to obtain 659.7 mg (1.83S mmol) ofa crude product of the above-entitled compound. The yield was 93.2%.

¹ H-NMR (300 MHz, CDC1₃)

δ: 1.78 (s, 3H), 2.97 (dd, 1H), 3,24 (dd, 1H), 3.87 (dd, 1H), 4.86 (m,1H), 5.05 (m, 2H), 5.55 (d, 1H), 7.18-7.39 (m, 1OH).

Mass spectrum (FAB) 360 (MH⁺)

Example 15

Production of(3S)-1-acetoxy-3-(N-benzyloxycarbonyl)amino-1-methylthio-2-oxo-4-phenylbutane:

404.5 mg (1.125 mmol) of(3S)-3-N-benzyloxycarbonylamino-1-hydroxy-l-methylthio-2-oxo-4-phenylbutanewas dissolved in 11 ml of dichloromethane and 0.27 ml of pyridine, and0.12 ml (1.69 mmol) of acetyl chloride was added thereto, while coolingit in an ice bath, and then stirred at room temperature for 3 hours and30 minutes. The reaction mixture was extracted with 20 ml of 0.5Nhydrochloric acid and 15 ml of dichloromethane. The resulting organiclayer was washed with 12 ml of a saturated aqueous solution of sodiumhydrogen carbonate and 15 ml of a saturated saline solution, and thendried with anhydrous sodium sulfate. This was filtered and concentrated,and the resulting residue was purified through silica gel columnchromatography (hexane/ethyl acetate=from 5/1 to 4/1) to obtain 413.3 mg(1.029 mmol) of the above-entitled compound. The yield was 91.5%. Theintegral ratio in ¹ H-NMR of the compound verified that the compound isa mixture of diastereomers of about 1:1.

¹ H-NMR (300 MHz, CDC1₃)

δ: 1.75 (s, 3/2H), 1.98 (s, 3/2H), 2.14 (s, 3/2H), 2.17 (s, 3/2H), 2.99(m, 1H), 3.17 (m, 1H), 4.97-5.29 (m, 4H), 6.01 (s, 1/2H), 6.15 (s,1/2H), 7 .17-7. 37 (m, 10H)

Mass spectrum (FA-B) 402 (MH⁺)

Example 16

Production of methylthio (3S)-(2R,S)-2-acetoxy-3-(N-benzyloxycarbonyl)amino-4-phenylbutyrate:

124.5 mg (0.310 mmol) of(3S)-1-acetoxy-3-N-benzyloxycarbonylamino-1-methylthio-2-oxo-4-phenylbutanewas dissolved in 3 ml of toluene, and 0.05 ml (0.334 mmol) of1,8-diazabicyclo 5.4.0!undec-7-ene was added thereto. After having beenstirred at room temperature for 1 hour and 55 minutes, this wasextracted with 15 ml of ethyl acetate and 7 ml of 1N hydrochloric acid.The resulting organic layer was washed with 7 ml of a saturated aqueoussolution of sodium hydrogen carbonate and 7 ml of a saturated salinesolution, then dried with anhydrous sodium sulfate, filtered andconcentrated. The resulting residue was purified through partitioning,silica gel thin-layer chromatography to obtain 121.4 mg (0.302 mmol) ofthe above-entitled compound. The yield was 97.5%. The integral ratio in¹ H-NMR of the compound verified that the ratio of the diastereomersconstituting it is about 6:4.

¹ H-NMR (300 MHz, CDC1₃)

δ: 2.18 (s, 3H), 2.25 (s, 6/5H), 2,31 (s, 9/5H), 2.77-2.99 (m, 2H), 4.53(m, 1H), 4.81 (br. d, 2/5H, --NH), 5.04 (d, 2H), 5.11 (br. d, 3/5H,--NH), 5.21 (d, 3/5H), 5.43 (d, 2/5H), 7.16-7.38 (m, 10H).

Mass spectrum (FAB) 402 (MH⁺)

Example 17

Production of(3S)-1-acetoxy-3-(N-benzyoxycarbonyl)amino-1-methylthio-2-oxo-phenylbutane(I, R¹ ═benzyloxycarbonyl, R² ═H, R³ ═benzyl, R⁴ ═acetyl, R⁵ ═methyl)

166.2 mg (0.462 mmol) of(3S)-3-(N-benzyoxycarbonyl)amino-1-methylsulfinyl-2-oxo-phenylbutane wasdissolved in 4.6 ml of dichloromethane, 0.5 ml of pyridine and 0.5 ml ofacetic anhydride, and 3 mg of 4-dimethylaminopyridine was added thereto,and stirred at room temperature for 17.5 hours. To the reaction mixturewas added 15 ml of ethyl acetate and 10 ml of 1N hydrochloric acid. Theresulting organic layer was washed with 10 ml of a saturated aqueoussolution of sodium hydrogencarbonate and 10 ml of a saturated salinesolution, and then dried with anhydrous sodium sulfate. This wasfiltered and concentrated, and the resulting residue was purifiedthrough silica gel thin-layer chromatography to obtain 124.5 mg (0.310mmol) of the above-entitled compound. The yield was 67.1%.

Example 18

Production of(3S)-1-acetoxy-3-(N,N-dibenzyl)amino-1-methylthio-2-oxo-phenylbutane (I,R¹ =benzyloxycarbonyl, R² =R³ =benzyl R⁴ =acetyl, R⁵ =methyl)

102.4 mg (0.252 mmol) of(3S)-3-(N,N-dibenzy)amino-1-methylsulfinyl-2-oxo-phenylbutane wasdissolved in 2 ml of dichloromethane, 0.2 ml of pyridine and 0.2 ml ofacetic anhydride, and 3 mg of 4-dimethylamino-pyridine was addedthereto, and stirred at room temperature for 10 days. To the reactionmixture was added 10 ml of ethyl acetate and 10 ml of 1N hydrochloricacid. The resulting organic layer was washed with 6 ml of water, 7 ml ofa saturated aqueous solution of sodium hydrogencarbonate and 7 ml of asaturated saline solution, and then dried with anhydrous sodium sulfate.This was filtered and concentrated, and the resulting residue waspurified through silica gel thin-layer chromatography to obtain 86.6 mg(0.193 mmol) of the above-entitled compound. The yield was 76.8%.

Example 19

Production of(3S)-3-(N,N-dibenzyl)amino-1-methylsulfinyl-2-oxo-4-phenylbutane (V, R¹=R² =R³ =benzyl, R⁵ =methyl)

3.55 g (91.0 mmol) of sodium amide was suspended in 53 ml oftetrahydorofuran and 10.8 ml (152 mmol) of dimethylsulfoxide and heatedat from 47° to 51° C. for 3 hours. The resulting suspension was cooledto -12° C. To this was dropwise added a solution of 13.63 g (96.9 wt %,30.33 mmol) of N,N-dibenzyl-L-phenylalanine methyl ester as dissolved in18 ml of tetrahydrofuran, while keeping it at -12° to -6° C. for 35minutes. After these were reacted at -12° to -8° C. for 1 hour, 110 mlof an aqueous solution of 10% citric acid and 44 ml of ethyl acetatewere added to the reaction mixture, which was thus subjected to phaseseparation. The organic layer was washed with 30 ml of a saturatedaqueous solution of sodium hydrogencarbonate and 30 ml of a saturatedsaline solution. This was dried with anhydrous sodium sulfate, filteredand concentrated to obtain the crude above-entitled compound. As theresult of HPLC analysis, 12.38 g (30.53 mmol) of the above-entitledcompound was obtained. The yield was 100%.

Example 20

Production of (3S)-3-(N,N-dibenzyl)amino-1-hydroxy-1-methylthio-2-oxo-phenylbutane hydrogen chloride salt (VI,R¹ ═R² ═R³ ═benzyl,R⁵ ═methyl)

The crude compound of(3S)-3-(N,N-dibenzyl)amino-1-methylsulfinyl-2-oxo-4-phenylbutane (12.38g (30.53 mmol)) obtained in Example 19 was dissolved in 68 ml of acetoneand 22.8 ml of dimethylsulfoxide, and 22.8 ml of 2N hydrochloric acidwas added thereto and stirred at 30° C. for 16 hours. While being cooledin an ice bath, this was neutralized with 50 ml of a saturated aqueoussolution of sodium hydrogencarbonate, and concentrated to removeacetone. Then the resulting solution was subjected to phase separationwith 60 ml of ethyl acetate. The organic layer was washed with 40 ml ofa saturated saline solution, and thereafter dried with anhydroussodiumsulfate. This was filtered and concentrated, and the resulting residuewas dissolved in 45.5 ml of ethyl acetate and 55 ml of hexane. To thiswas dropwise added 9.1 ml of 4N hydrogen chloride solution in ethylacetate. The resulting solid was filtered and washed with 45 ml of ethylacetate/hexane=1/2, and dried to obtain 11.48 g of a crude product ofthe above-entitled compound.

Example 21

Production of (3S)-1-acetoxy-3-(NN-dibenzyl)amino-1-methylthio-2-oxo-phenylbutane (I, R¹ ═R² ═R³ ═benzylR⁴ ═acetyl, R⁵ ═methyl)

11.48 g of the crude product of (3S)-3-(N,N-dibenzyl)amino-1-hydroxy-l-methylthio-2-oxo-phenylbutane hydrogen chloride saltas obtained in Example 20 was dissolved in 52 ml of dichloromethane and4.62 ml of pyridine, and 2.22 ml of acetyl chloride was added thereto,while cooling in an ice bath for 5 minutes, and stirred at 10° C. for 1hour. The reaction mixture was extracted with 30 ml of an aqueoussolution of 10% citric acid. The resulting organic layer was washed with30 ml of a saturated aqueous solution of sodium hydrogencarbonate and 30ml of a saturated saline solution, and then dried with anhydrous sodiumsulfate. This was filtered and concentrated to obtain the crudeabove-entitled compound. As the result of HPLC analysis, this crudeproduct contained 9.395 g (20.99 mmol) of the above-entitled compound,and the yield was 69.2% (2 steps).

Example 22

Production of methylthio (2S,3S)-2-acetoxy-3-(N,N-dibenzy 1)amino-4-phenylbutyrate (II, R¹ ═R² ═R³ ═benzyl, R⁴ ═acetyl, R⁵ ═methyl)

The crude compound of(3S)-l-acetoxy-3-(N,N-dibenzyl)amino-1-methylthio-2-oxo-phenylbutane(9.39S g (20.99 mmol)) as obtained in Example 21 was dissolved in 45 mlof N,N-dimethylformamide and cooled to -31° C., and a solution of 641 mg(4.21 mmol) of 1,8-diazabicyclo 5,4,0! undec-7-ene as dissolved in 3 mlof N,N-dimethylformamide was added thereto for 10 minutes. After havingbeen stirred at -30° C. for 16 hours, this was extracted with 50 ml ofan aqueous solution of 10% citric acid and 77 ml of ethyl acetate. Theresulting organic layer was washed with 50 ml of water+10 ml of asaturated saline solution, 30 ml of a saturated aqueous solution ofsodium hydrogencarbonate, and 30 ml of a saturated saline solution inthat order, and then dried with anhydrous sodium sulfate. This wasfiltered and concentrated to the crude above-entitled compound. As theresult of HPLC analysis, the ratio of diastereomers constituting it, of(2S,3S):(2R,3S), is about 89:11 and 8.101 g (18.10 mmol) of(2S,3S)-diastereomer was obtained. The yield of (2S,3S)-diastereomer was86.2%.

Example 23

Production of (2S,3S)-3-(N,N-dibenzyl)amino-2-hydroxy-4-phenyl butyricacid dicyclohexylamine salt (VII,R¹ ═R² ═R³ ═benzyl, R⁷ ═H)

The crude compound of methylthio(2S,3S)-2-acetoxy-3-(N,N-dibenzyl)amino-4-phenylbutyrate (8.101 g (18.10mmol)) as obtained in Example 22 was dissolved in 90 ml of methanol, and36 ml of 2N aqueous solution of sodium hydroxide was added thereto andstirred at room temperature for 3.5 hours. After these were concentratedto remove methanol, 50 ml of dichloromethane and 12 ml of 6Nhydrochloric acid to adjust to pH 1.9 were added to the reactionmixture. After separation, the resulting organic layer was washed with30 ml of saturated saline solution, and then dried with anhydrous sodiumsulfate. This was filtered and concentrated, and the resulting residuewas dissolved in 50 ml of acetone. After filtration to remove theinsoluble matter and washing it with 30 ml of acetone, to this filtratewas dropwise added 4.43 g (24.43 mmol) of dicyclohexylamine and theresulting crystal was filtered and washed with 30 ml of acetone, anddried under vacuum to obtain 9.02 g (95.0 wt %, 15.39 mmol) of theabove-entitled compound. The yield was 85.0%.

¹ H-NMR (300 MHz, CDC1₃)

δ: 0.95-1.42 (m, SH), 1.50-1.97 (m, 5H), 2.48 (dd, 1H), 2.77 (m, 2H),3.03 (dd, 1H), 3.50 (ddd, 1H), 3.60 (d,2H), 4.02 (d, 2H), 4.44 (d, 1H),6.95-7.35 (m, 15H)

¹³ C-NMR (75 MHz, CDC1₃)

δ: 24.61, 25.07, 28.96, 32.69, 52.29, 54.09, 62.06, 69.93, 125.50,126.21, 127.68, 127.77, 128.55, 129.73, 140.63, 140.83, 178.18.

Mass spectrum (FAB) 557 (MH⁺)

Example 24

Production of(3S)-3-(N,N-dibenzyl)amino-1-methylsulfinyl-5-methyl-2-oxo-hexane (V, R¹═R² ═benzyl, R³ ═isobutyl, R⁵ ═methyl)

1.00 g (25.63 mmol) of sodium amide was suspended in 10 ml ofdimethylsulfoxide and heated at from 50° to 60° C. for 30 minutes. 10 mlof tetrahydrofuran was added to the resulting solution and cooled to -5°C. To this was dropwise added a solution of 3.38 g (10.39 mmol) ofN,N-dibenzyl-(L)-leucine methyl ester as dissolved in 6.5 ml oftetrahydrofuran, while keeping it at -5° C. for 40 minutes. After thesewere reacted at -5° C. for 1 hour and 20 minutes, 40 ml of an aqueoussolution of 10% citric acid and 50 ml of ethyl acetate were added to thereaction mixture which was thus subjected to phase separation. Theorganic layer was washed with 30 ml of a saturated aqueous solution ofsodium hydrogencarbonate and 20 ml of a saturated saline solution. Thiswas dried with anhydrous sodium sulfate, filtered and concentrated, andthe resulting residue was purified through silica gel columnchromatography (hexane/ethyl acetate=1/1 to 1/3 ) to obtain 3.86 g ofthe above-entitled compound. The yield was 100%. The integral ratio in ¹H-NMR of the compound verified that the ratio of the diastereomersconstituting it is about 1:1.

¹ H-NMR (300 MHz, CDC1₃)

δ: 0.80 (d, 3/2H), 0.86 (d, 3/2H), 0.89 (d, 3/2H), 0.90 (d, 3/2H),1.36-1.50 (m, 2H), 1.83 (m, 1H), 2.57 (s,3/2H), 2.61 (s, 3/2H), 3.34(br. d, 1H), 3.48 (dd, 2H), 3.72 (br. d, 2H), 3.81-3.96 (m, 3/2H), 4.09(d, 1/2H), 7.24-7.39 (m, 10H).

Mass spectrum (ESI) 372 (MH⁺)

Example 25

Production of(3S)-3-(N,N-dibenzyl)amino-1-hydroxy-1-methylthio-5-methyl-2-oxo-hexane(VI,R¹ ═R² ═benzyl, R³ ═isobutyl, R⁵ ═methyl)

2.35 g (6.324 mmol) of(3S)-3-(N,N-dibenzyl)amino-1-methylsulfinyl-5-methyl-2-oxo-hexane wasdissolved in 19 ml of dimethylsulfoxide, and 4.74 ml of 2N hydrochloricacid was added thereto and stirred at 30° C. for 14 hours. While beingcooled in an ice bath, this was neutralized with 15 ml of a saturatedaqueous solution of sodium hydrogencarbonate, and then subjected tophase separation with 30 ml of ethyl acetate and 20 ml of water. Theorganic layer was washed with 20 ml of water and 20 ml of a saturatedsaline solution in that order, and thereafter dried with anhydroussodium sulfate.

This was filtered and concentrated to obtain 2.16 g of a crude productof the above-entitled compound. The integral ratio in ¹ H-NMR of thecompound verified that the compound is a mixture of diastereomers ofabout 10:1. The data of the major diastereomerase shown below.

¹ H-NMR (300 MHz, CDC1₃)

δ: 0.85 (d, 3/2H), 0.94 (d, 3/2H), 1.35-1.50 (m, 2H), 1.74 (s, 3H), 1.93(m, 1H), 3.41 (d, 2H), 3.68 (d, 2H), 3.82-3.90 (m, 2H), 5.50 (br. s,1H), 7.23-7.36 (m, 10H).

Example 26

Production of(3S)-1-acetoxy-3-(N,N-dibenzylamino-1-methylthio-5-methyl-2-oxo-hexane(I, R¹ ═R² ═benzyl, R³ ═isobutyl, R⁴ ═acetyl, R⁵ ═methyl)

1.66 g (4.47 mmol) of the crude product of(3S)-3-(N,N-dibenzyl)amino-1-hydroxy-1-methylthio-5-methyl-2-oxo-hexaneas obtained in Example 25 was dissolved in 16 ml of dichloromethane and0.54 ml of pyridine, and 0.38 ml of acetyl chloride was added thereto,while cooling in an ice bath, and stirred at room temperature for 1hour. The reaction mixture was extracted with 15 ml of an aqueoussolution of 10% citric acid and 10 ml of dichloromethane as addedthereto. The resulting organic layer was washed with 15 ml of asaturated aqueous solution of sodium hydrogencarbonate and 15 ml of asaturated saline solution, and then dried with anhydrous sodium sulfate.This was filtered and concentrated, and the resulting residue waspurified through partitioning, silica gel column chromatography toobtain 1.48 g (3.58 mmol) of above-entitled compound. The yield was80.1%. The integral ratio in ¹ H-NMR of the compound verified that thecompound is a mixture of diastereomers of about 10:1. The data of themajor diastereomer are shown below.

¹ H-NMR(300 MHz, CDC1₃)

δ: 0.83 (d,3H), 0.91 (d,3H), 1.38-1.47 (m,2H), 1.84 (s,3H), 1.86 (m,1H), 2.18 (s,3H), 3.43 (d,2H), 3.72 (d,2H), 3.84 (dd, 1H), 6.48 (s, 1H),7.22-7.37(m,10H).

Mass spectrum (ESI) 414 (MH⁺)

Example 27

Production of methylthio (2S,3S)-2-acetoxy-3-(N,N-dibenzyl)amino-5-methylhexanoate (II, R¹ ═R² ═benzyl, R³ ═isobutyl, R⁴ ═acetyl,R⁵ ═methyl)

0.61 g (1.48 mmol) of (3S)-1-acetoxy-3-(N,N-dibenzyl)amino-1-methylthio-5-methyl-2-oxo-hexane was dissolved in 7.5 ml ofN,N-dimethylformamide and cooled to -30° C., and 0.066 ml of1,8-diazabicycl 5,4,0!undec-7-ene was added thereto. After having beenstirred at -30° C. for 15.5 hours, this was extracted with 20 ml of anaqueous solution of 10% citric acid and 30 ml of ethyl acetate. Theresulting organic layer was washed with 20 ml of a saturated aqueoussolution of sodium hydrogen-carbonate and 20 ml of a saturated salinesolution, and then dried with anhydrous sodium sulfate. This wasfiltered and concentrated, and the resulting residue was purifiedthrough partitioning, silica gel column chromatography to obtain 0.60 gof above-entitled compound. The yield was 98%. The integral ratio in ¹H-NMR of the compound verified that the ratio of diastereomersconstituting it of (2S,3S):(2R,3S), is about 95:5. The data of the majordiastereomer((2S,3S)-form) are shown below.

¹ H-NMR(300 MHz, CDC1₃)

δ: 0.37 (d, 3H), 0.87 (d, 3H), 1.01 (m, 1H), 1.76-1.86 (m, 2H), 2.23 (s,3H), 2.26 (s, 3H), 3.25 (m, 1H), 3.31 (d, 2H), 3.592 (d, 2H), 5.83 (d,1H), 7.21-7.33 (m, 10H)

Mass spectrum (ESI) 414 (MH⁺)

Having now fully described the invention, it will be apparent to one ofordinary skill in the art that many changes and modifications can bemade thereto without departing from the spirit or scope of the inventionas set forth herein.

This application is based on JP 257497/1995 filed in Japan on Oct. 4,1995. The full text of the priority document is incorporated herein byreference.

What is claimed as new and desired to be secured by letters patent ofthe U.S. is:
 1. A compound represented by formula (II): ##STR10##wherein R¹ represents a linear, branched or cyclic alkanoyl group havingfrom 2 to 18 carbon atoms, a linear, branched or cyclic alkoxycarbonylgroup having from 2 to 18 carbon atoms, an aralkyloxycarbonyl grouphaving from 7 to 18 carbon atoms, or a benzyl group, or represents,together with R², a residue of a dibasic acid having from 8 to 18 carbonatoms;R² represents a hydrogen atom or a benzyl group, or represents,together with R¹, a residue of a dibasic acid having from 8 to 18 carbonatoms; R³ represents a linear, branched or cyclic alkyl group havingfrom 1 to 18 carbon atoms, an aralkyl group having from 7 to 18 carbonatoms; or an aryl group having from 6 to 18 carbon atoms; R⁴ representsa linear, branched or cyclic alkanoyl group having from 2 to 18 carbonatoms, or an arylcarbonyl group having from 7 to 18 carbon atoms; and R⁵represents an alkyl group having 1 or 2 carbon atoms, an aryl grouphaving from 6 to 18 carbon atoms, or an aralkyl group having from 7 to18 carbon atoms.
 2. The compound of claim 1, having a(3S)-configuration.
 3. The compound of claim 1, having a(3R)-configuration.
 4. The compound of claim 1, wherein R¹ represents alinear, branched or cyclic alkanoyl group. having from 2 to 18 carbonatoms.
 5. The compound of claim 1, wherein R¹ represents a linear,branched or cyclic alkoxycarbonyl group having from 2 to 18 carbonatoms.
 6. The compound of claim 1, wherein R¹ represents anaralkyloxycarbonyl group having from 7 to 18 carbon atoms.
 7. Thecompound of claim 1, wherein R¹ represents a benzyl group.
 8. Thecompound of claim 1, wherein R¹ represents, together with R², aphthaloyl group.
 9. The compound of claim 1, wherein R² represents ahydrogen atom.
 10. The compound of claim 1, wherein R² represents abenzyl group.
 11. The compound of claim 1, wherein R³ represents alinear, branched or cyclic alkyl group having from 1 to 18 carbon atoms.12. The compound of claim 1, wherein R³ represents an aralkyl grouphaving from 7 to 18 carbon atoms.
 13. The compound of claim 1, whereinR³ represents an aryl group having from 6 to 18 carbon atoms.
 14. Thecompound of claim 1, wherein R⁴ represents a linear, branched or cyclicalkanoyl group having from 2 to 18 carbon atoms.
 15. The compound ofclaim 1, wherein R⁴ represents an arylcarbonyl group having from 7 to 18carbon atoms.
 16. The compound of claim 1, wherein R⁵ represents analkyl group having 1 or 2 carbon atoms.
 17. The compound of claim 1,wherein R⁵ represents an aryl group having from 6 to 18 carbon atoms.18. The compound of claim 1, wherein R⁵ represents an aralkyl grouphaving from 7 to 18 carbon atoms.